1. Field of the Invention
The invention relates to an extrusion system and a process for minimizing color change times in the extrusion of thermoplastics.
2. Description of the Related Art
The usual procedure in the manufacture of colored extrudates is to supply the extruder with a mixture of a non-pigmented base molding mass and a master batch which contains the pigment in high concentration. Mixing can take place both off-line in batches in a separate mixer, or in-line by parallel metering of the two components into the extruder hopper.
In case of a color change, generally no further master batch is metered in until the color has been washed out of the system. If necessary, a cylinder cleaning agent such as a molding mass with high viscosity can also be passed through for cleaning. Afterwards, a master batch with a different color is used. The color change has been completed once the new extrudate uniformly exhibits the new color. The extrudate produced during the color change generally cannot be sold.